1. Technical Field
The multiple embodiments disclosed herein relate to a method for detecting a fault on a data line in a bus system in a two-conductor data network having at least two control units.
2. Background Art
In the case of such two-wire data buses, such as a CAN-Bus (derived from Control Area Network), for which the properties are specified in ISO 11898, individual data bits are transmitted differentially on the two lines of the bus. In a quiescent state, both lines of the bus have about the same potential, since the two lines are coupled to one another through a terminating resistor. A dominant bit is actively transmitted from a transmitter on the bus by enabling a driver current. This transmission occurs differentially, which means that the potential of one line of the bus is raised and the potential of the other line of the bus is lowered. A recessive bit is transmitted by a transmitter by turning off the driver current. In the following discussion, we assume that the two bus lines remain at approximately the same potential.
Different kinds of errors can occur in data buses of this type. Short circuits can arise in the individual conductors with respect to a reference potential and also with respect to one another. DE 100 59 769 A1 discloses that known circuit arrangements analyze the potentials of the conductors and attempt to infer whether such short circuits are present.
In a circuit element known from U.S. Pat. No. 5,488,306, the difference in potentials of the two bus lines is also evaluated. A concrete example of a circuit is presented in this publication that allows for definite error recognition to occur without reacting to ground offsets of the bus conductors resulting from error recognition by differential current measurement and not by voltage measurement.
A method for detecting the ground offsets of portions of a network system is disclosed in DE 102 25 556 A1, in particular for testing the ground contact between networked control units, wherein data are sent and received through at least one bus system. Thus, in the quiescent state of at least one bus conductor provided for receiving the data or at least one receiver line, the voltage is sampled after the passage of a specifiable first time interval and is compared with at least one specifiable threshold or reference potential value. If the threshold value is exceeded, it then produces a ground fault signal by which the quiescent state of the at least one bus conductor is evaluated. The circuit is relatively complex and complicated, and thus expensive.
An important requirement for high-speed CAN systems in motor vehicles is the diagnosis of the conductor lines, which also results from the previously mentioned documents. The prevalent solutions consist in that a diagnosis is carried out in integrated circuits, namely in central interface modules. Such interface modules are relatively expensive. The high speed TJA1041A and TJA1040-CAN-transceivers are cited for example. It is obvious from the specification sheets for these integrated circuits that two resistors (each 60Ω) are connected between the data lines such that their connection point to ground is switched through a condenser and connected with an input of the transceiver. Stabilization is to be achieved in this manner.